Flow rate-responsive fuel mixture control device with servomechanism

ABSTRACT

In the air suction tube of a fuel injection system associated with an internal combustion engine, there is displaceably held a control member which regulates a flow passage section for the air and meters the fuel in response to the change in the flow rate of air in the suction tube. The change in the static air pressure due to the change in the flow rate is utilized as an input force to control a servocircuit whose relatively large output force is used directly to displace said control member.

United States Patent lnventor Konrad Eckert Stuttgart-Bad, Germany Appl.No. 782,689 Filed Dec. 10, 1968 Patented June 29, 1971 Assignee RobertBosch G.m.b.II.

Stuttgart, Germany Priority Jan. 5, 1968 Germany P 16 01 360.8

FLOW RATE-RESPONSIVE FUEL MIXTURE CONTROL DEVICE WITH SERVOMECIIANISM 9Claims, 1 Drawing Fig.

US. Cl

Int. Cl Field of Search [56] References Cited UNITED STATES PATENTS1,550,717 8/1925 Towle .4 137/220 1,620,131 3/1927 Price 137/487 X2,330,650 9/1943 Weiche 261/50 2,820,364 1/1958 Bevins et al. 261/50FOREIGN PATENTS 885,821 12/1961 Great Britain 137/220 938,222 10/1963Great Britain 137/220 Primary Examiner-Robert G. Nilson Attorney-EdwinE. Greigg ABSTRACT: In the air suction tube of a fuel injection systemassociated with an internal combustion engine, there is displaceablyheld a control member which regulates a flow passage section for the airand meters the fuel in response to the change in the flow rate of air inthe suction tube. The change in the static air pressure due to thechange in the flow rate is utilized as an input force to control aservocircuit whose relatively large output force is used directly todisplace said I control member.

PATENTFflmmzsmn 3,589,384

Konrad ECKERT his ATTO Y lFLOW RATE-RESPONSIVE FUEL MIXTURE CONTROLDEVICE WITH SERVOMECIIANISM BACKGROUND OF THE INVENTION This inventionrelates to fuel injection systems associated with externally ignitedinternal combustion engines for particular use in motor vehicles. Saidsystems are of the type wherein the supply of air is controlled by anarbitrarily operable throttle member (butterfly valve) disposed in thesuction tube and wherein the unmixed air in the suction tube flows pasta displaceably held control member at least partially disposed withinthe suction tube-The control member, by virtue of its displacement,which is a function of the variations in the flow rate of air, varies aflow passage section in the suction tube. The fuel is, at a constantpressure drop, continuously metered at a variable throttle as a functionof the position of said control member. a i

The purpose of fuel injection systems of the above type is to providefavorable mixture ratios permitting a complete combustion of the fuel atthe highest possible efficiency of the engine with the lowest possiblefuel consumption.

In known fuel injection systems of the afore-outlined type, the fuel ismetered bya control member which is positioned as a function of the flowrate of air and which automatically regulates an air flow passagesection in the suction tube, so that there is maintained a substantiallyconstant static air pressure in the narrowest portion of the flowpassage section. Such a device is described in British Pat. No.1,066,721.

For displacing the control member, one of its sides is exposed to theforce of a spring and to the static pressure prevailing at the narrowestportion of the flow passage section and its other side is exposed to thetotal pressure of the flowing air.

It is, however, disadvantageous to actuate the control member bypneumatic means directly, since the force effect of the air caused bypressure variations is small. Consequently, due to the unavoidablefrictional effects, the positioning of the control member is not alwaysan exact function of the flow rate of air.

To remedy this disadvantage the solution presents itself to enlarge thesurfaces exposed to air pressures. Such an increase of the surfaces,however, would be inconvenient since, in the first place, it wouldrequire large volumes and, secondly, the pressure variations at thenarrowest portion of the flow passage section would occur only slowlybecause relatively large volumes of air have to be exchanged. As aresult, the control member would assume its position at low speed. Also,the masses to be moved as well as the required space would significantlyincrease.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention toprovide an improved fuel injection system of the afore-outlined typewherein the control member rapidly assumes its new, desired position.

Briefly stated, according to the invention, the control member isdisplaceable by means of a hydraulic servo mechanism including a servoelement which is moved by a pneumatic actuator. The latter operates as afunction-of the static air pressure prevailing at the at leastapproximately narrowest portion of the flow passage section which, inturn, is varied by the control member. The servo element and thepneumatic actuator are interconnected in such a manner that the controlmember, in case of an increased static pressure of the air, is displacedin a direction to decrease the flow passage section for the air and,conversely, when the static air pressure decreases, the control memberis displaced in the opposite direction and thus increases the flowpassage section. First, there is provided a closed servo circuit(forming part of the servomechanism) and, secondly, the static pressureregulated by this servocircuit remains substantially constant at thenarrowest portion of the flow passage section.

The invention will be better understood as well as other objects andadvantages will become more apparent from the ensuing detailedspecification of a preferred, although exemplary, embodiment of theinvention taken in conjunction with the sole figure showing theembodiment in axial section.

DESCRIPTION OF THE EMBODIMENT The air required for the combustion passesin the direction of the arrow through a two-part suction tube 1 andflows past a control member generally indicated at 2 and an arbitrarilyactuated butterfly valve 3 towards the cylinders (not shown) of aninternal combustion engine (not shown). The fuel is drawn from a tank 4through a filter 5 by means of a pump 6 and, flowing past a bypass 7provided with an overflow valve 8, is led through a pressure conduit 9under constant pressure to a fuel metering device 10 illustrated only ina schematic manner. A fuel conduit 11 leads from the metering device 10to one or several nozzles 12 through which the fuel, preferably shortlyupstream of the cylinder or cylinders, is injected into the suction tube1.

The control member 2 comprises a hollow cylinder axially slidably heldon a guiding tube 14 and coaxially disposed in a funnel-shaped portion13 of the suction tube 1. To the cylinder 15 there is internally andaxially secured a piston 16 slidably disposed within the guiding tube14.

The cylinder 15 is provided with an upstream narrowing streamlinedconical outer face which, together with the funnel-shaped portion 13,forms a narrow flow passage section 17 for the air. An outer portion ofcylinder 15 is formed .as a cam 18 associated with a follower pin 19which, upon displacement of cylinder 15, actuates a throttle (not shown)in the fuel metering device 10 for controlling the quantity of fueladmitted to conduit 11.

The guiding tube 14, which at its downstream end is closed fluidtight bya threaded screw cap 20, is pressfitted into a sleeve 21 rigidly heldcoaxially within the suction tube 1 by means of webs 22.

In the space 23 of the guiding tube 14 there is disposed a spring 24which, at one end, is attached to the piston 16 and, at the other end,is freely rotatably hooked to the screw cap 20. The spring 24 tends todisplace the piston 16 together with the cylinder 15 in a downstreamdirection.

A fuel conduit 25 communicates with space 23 so that the downstreamterminal face 26 of the piston 16 is adapted to be exposed to the fuelpressure prevailing in conduit 9, as it will become apparenthereinafter.

The inner space 27 of the cylinder 15 communicates with a conduit 27athrough which the fuel, leaking past piston 16 from space 23, isreturned to tank 4.

The admission of fuel to the fuel conduit 25 is controlled by means of aservo element formed as a piston plunger 29 disposed in valve block 28and displaceable by a pneumatically actuated membrane 30 to which it isattached.

The membrane 30 serves as a septum separating spaces 31a and 31b invalve block 28. The membrane 30 is, on its upper side, affected by thestatic pressure of the air prevailing in the flow passage section 17 andby the force of a compression spring 33 and, on its lower side, by theair pressure prevailing in the space 350 defined by portion 35 of thesuction tube 1 downstream of the flow passage section 17. The staticpressure prevailing in the approximately narrowest portion of the flowpassage section 17 is admitted to space 310 through port 32, while thepressure in space 35a is admitted to space 31b through conduit 34. Theflow passage section of space 35a is relatively large; thus the airvelocity therethrough is relatively small. As a result, an at leastapproximately total pressure of the air (static pressure plus dynamicpressure) prevails in conduit 34.

Depending upon the position of the piston plunger 29, the fuel conduit25 is either connected with the pressure conduit 9 through a conduit 36,or is connected with the tank 4 across a return conduit 37, or isblocked altogether.

OPERATION OF THE EMBODIMENT Any change of the flow rate in the suctiontube 1 also causes a variation in the static pressure prevailing in theflow passage section 17. This pressure variation is, due to theinterconnecting port 32, followed in space 31a. Membrane 30 yields inresponse to this pressure variation affecting its upper face and, as aresult, the piston plunger 29 is displaced.

Thus, if the static pressure increases in flow passage section 17, thepiston plunger 29 travels downwardly from its position shown in thefigure, whereby communication is established between conduits 25 and 36,so that the liquid pressure prevailing in conduit 9 is transmitted tospace 23. This pressure in the space 23 causes the piston 16, togetherwith with cylinder 15, to be displaced upstream, decreasing thereby theflow passage section 17.

Should the static pressure fall in flow passage section 17, the pistonplunger 29 moves upwardly; as a result, communication is establishedbetween the conduit 25 and return conduit 37. Thus, the fuel in thespace 23 is now neither confined nor pressurized, so that tension spring24 can cause a downstream displacement of piston 16 together with thecylinder enlarging thereby the flow passage section 17. The downstreamdisplacement of piston 16 causes a part of the fuel in space 23 to beforced across the conduit 25 and drained through return conduit 37 intotank 4.

As soon as the static pressure attains its original value by virtue ofthe change of the flow passage section 17, the piston plunger 29 returnsinto its original position closing conduit 25. The fuel now confined inconduit 25 and space 23 resists the force of spring 24 and,consequently, the piston 16 stops.

It is thus seen that the aforedescribed servomechanism includes aservocircuit controlled by an input force that is constituted by thestatic pressure of air prevailing in flow passage section 17.

It is to be understood that means may be provided for an arbitraryadjustment of the effective length of spring 33 whereby its force ischanged, thus affecting the function between the static pressure in flowpassage section 17 and the position of the control member l5, l6.

ADVANTAGES OF THE INVENTION The servo force utilized for that meansdisplacement of the control member 15, 16 is large so that the operationof the device is substantially independent of frictional forces.

The use of the servo force also means an increased camming force for thedisplacement of follower pin 19 effecting the metering of the fuel.

Further, the throttling losses in the flow passage section 17 may bemaintained at a small value since a smaller pressure drop is necessaryfor the actuation of piston plunger 29 by membrane 30 than would berequired were the pressure drop directly applied for the displacement ofthe cylinder 15.

Since small pressure variations control large output forces, changes inthe flow rate of air cause high speed settings.

The system operates independently of the designed structural position ofthe control member 15, 16.

Accelerating forces (engine vibrations, braking retardations) as well asair vibrations in the suction tube 1 have practically no effect sincethey are hydraulically dampened by virtue of the piston 16.

lclaim:

1. A fuel injection system associated with an internal combustionengine, comprising A. a suction tube for drawing air,

B. a throttle in said suction tube for arbitrarily controlling the flowrate of air therein,

C. a fuel metering device including a throttle,

D. a control member at least partially disposed in said suction tube andheld displaceably therein, said control member being displaced inresponse to changes in said flow rate; said control member, by virtue ofits displacement, simultaneously varying an air flow passage section insaid suction tube and controlling the throttle of said fuel meteringdevice, I E. a hydraulic servo mechanism for displacing said controlmember and including 1. displaceable means responsive to the changes inthe static air pressure prevailing in the approximately narrowest partof said flow passage section, and

2. a servocircuit controlled by said displaceable means for moving saidcontrol member in a direction of decreasing said flow passage sectionwhen said static pressure increases and in a direction of increasingsaid flow passage section when said static pressure decreases; saidservo mechanism tending to maintain constant said static pressure at theapproximately narrowest portion of said flow passage section.

2. The improvement as defined in claim 1, wherein said displaceablemeans includes an actuator member directly affected by said staticpressure and a servo element movable by said actuator member forcontrolling said servo circuit.

3. The improvement as defined in claim 2, wherein said suction tubeincludes a funnel-shaped portion, a guiding tube coaxially and fixedlyheld in said suction tube, said control member includes a hollowcylinder axially slidably held on said guiding tube and a piston fixedlysecured to the inside of said cylinder and slidably received in saidguiding tube, said piston is directly affected by the opposing forcesofa hydraulic fluid in said servocircuit and of a spring disposed withinsaid guiding tube.

4. The improvement as defined in claim 3, wherein said actuator memberis a membrane, one side of which is exposed to said static air pressure,the other side of which is exposed to the total air pressure prevailingin said suction tube.

5. The improvement as defined in claim 4, wherein the force of saidstatic pressure is aided by a spring in engagement with said membrane.

6. The improvement as defined in claim 3, wherein said servo element isformed by a piston plunger attached to and movable by said actuatormember; said piston plunger is, when said static pressure increases,adapted to establish communication between the inside of said guidingtube and a means containing hydraulic fluid under pressure, causingthereby to displace said piston and said cylinder in an upstreamdirection to decrease said flow passage section; said piston plunger is,when said static pressure decreases, adapted to establish communicationbetween the inside of said guiding tube and a tank means, causingthereby said piston and said cylinder to be displaced by said spring ina downstream direction to increase said flow passage section.

7. The improvement as defined in claim 6, wherein said piston plunger isadapted to interrupt communication both between the inside of saidguiding tube and said means containing hydraulic fluid and between theinside of said guiding tube and said tank means to confine hydraulicfluid inside said guiding tube for arresting the motion of said pistonand said cylinder when said static pressure assumes its original value.

8. The improvement as defined in claim 7, wherein said hydraulic fluidis fuel used for combustion in said engine, said tank means isconstituted by a fuel tank and said means containing hydraulic fluidunder pressure is a conduit communicating with said fuel tank andcontaining fuel pressurized by a fuel pump that simultaneously deliversfuel to said fuel metering device.

9. The improvement as defined in claim 3, wherein the outer face of saidcylinder is, in its upstream portion, conically shaped and defines,together with said funnel-shaped portion of said suction tube, said flowpassage section varied by said control member.

1. A fuel injection system associated with an internal combustionengine, comprising A. a suction tube for drawing air, B. a throttle insaid suction tube for arbitrarily controlling the flow rate of airtherein, C. a fuel metering device including a throttle, D. a controlmember at least partially disposed in said suction tube and helddisplaceably therein, said control member being displaced in response tochanges in said flow rate; said control member, by virtue of itsdisplacement, simultaneously varying an air flow passage section in saidsuction tube and controlling the throttle of said fuel metering device,E. a hydraulic servo mechanism for displacing said control member andincluding
 1. displaceable means responsive to the changes in the staticair pressure prevailing in the approximately narrowest part of said flowpassage section, and
 2. a servocircuit controlled by said displaceablemeans for moving said control member in a direction of decreasing saidflow passage section when said static pressure increases and in adirection of increasing said flow passage section when said staticpressure decreases; said servo mechanism tending to maintain constantsaid static pressure at the approximately narrowest portion of said flowpassage section.
 2. a servocircuit controlled by said displaceable meansfor moving said control member in a direction of decreasing said flowpassage section when said static pressure increases and in a directionof increasing said flow passage section when said static pressuredecreases; said servo mechanism tending to maintain constant said staticpressure at the approximately narrowest portion of said flow passagesection.
 2. The improvement as defined in claim 1, wherein saiddisplaceable means includes an actuator member directly affected by saidstatic pressure and a servo element movable by said actuator member forcontrolling said servo circuit.
 3. The improvement as defined in claim2, wherein said suction tube includes a funnel-shaped portion, a guidingtube coaxially and fixedly held in said suction tube, said controlmember includes a hollow cylinder axially slidably held on said guidingtube and a piston fixedly secured to the inside of said cylinder andslidably received in said guiding tube, said piston is directly affectedby the opposing forces of a hydraulic fluid in said servocircuit and ofa spring disposed within said guiding tube.
 4. The improvement asdefined in claim 3, wherein said actuator member is a membrane, one sideof which is exposed to said static air pressure, the other side of whichis exposed to the total air pressure prevailing in said suction tube. 5.The improvement as defined in claim 4, wherein the force of said staticpressure is aided by a spring in engagement with said membrane.
 6. Theimprovement as defined in claim 3, wherein said servo element is formedby a piston plunger attached to and movable by said actuator member;said piston plunger is, when said static pressure increases, adapted toestablish communication between the inside of said guiding tube and ameans containing hydraulic fluid under pressure, causing thereby todisplace said piston and said cylinder in an upstream direction todecrease said flow passage section; said piston plunger is, when saidstatic pressure decreases, adapted to establish communication betweenthe inside of said guiding tube and a tank means, causing thereby saidpiston and said cylinder to be displaced by said spring in a downstreamdirection to increase said flow passage section.
 7. The improvement asdefined in claim 6, wherein said piston plunger is adapted to interruptcommunication both between the inside of said guiding tube and saidmeans containing hydraulic fluid and between the inside of said guidingtube and said tank means to confine hydraulic fluid inside said guidingtube for arresting the motion of said piston and said cylinder when saidstatic pressure assumes its original value.
 8. The improvement asdefined in claim 7, wherein said hydraulic fluid is fuel used forcombustion in said engine, said tank means is constituted by a fuel tankand said means containing hydraulic fluid under pressure is a conduitcommunicating with said fuel tank and containing fuel pressurized by afuel pump that simultaneously delivers fuel to said fuel meteringdevice.
 9. The improvement as defined in claim 3, wherein the outer faceof said cylinder is, in its upstream portion, conically shaped anddefines, together with said funnel-shaped portion of said suction tube,said flow passage section varied by said control member.